ECONOMIC POTENTIAL OF PEGMATITES IN MALAWI By

Grain W. P. Malunga FIMMM

Mineral Resources and Environmental Management Expert

Abstract

Malawi is underlain by basement metamorphic rocks intruded mainly by basic, granitic and syenitic

rocks and overlain by sedimentary rocks. Most of these pegmatites are granitic with abundant quartz,

feldspar and mica.

So far, valuable minerals such as beryl, tourmaline, zircon and garnets have been observed. There exist

potential for discovery of other rare and industrial minerals.

INTRODUCTION

Pegmatites are course grained granitic rocks that occur as dykes and form narrow ridges or small hills.

Most pegmatites contain abundant quartz, feldspar and mica. It is important to note that there exist

other pegmatites derived from plutonic rocks such as gabbro and syenite. They contain important

accessory minerals in form of gemstones or rare minerals.

Figure 1: Kacheure pegmatite displaying quartz plus feldspar, mica and quartz plus feldspar zoning

These accessory and valuable minerals include beryl, tourmaline, spodumene, garnet and topaz.

Industrial minerals from these rocks include quartz and mica while rare minerals that can also be

formed in them include columbite and tantalite.

This paper tries to inform prospectors that they will definitely encounter these minerals and tries to

describe their physical and chemical characteristics.

PEGMATITE MINERALS

GEMSTONES Gemstones found in Malawi pegmatite include: amazonite, apatite, beryl (aquamarine, chrysoberyl, emerald) garnet, kunzite, lepidolite, spodumene, topaz, tourmaline, zircon and many others. Large crystals of excellent quality material are often found in pegmatite. Gemmstones obtain their colour from their own makeup (idiochromatic) or from trace elements (impurities) such as chromium, lithium, copper, iron, manganese and vanadium giving them an allochromatic characteristic. Natural dispersion of light (pseudochromatic) through surface reflection can also give colour to gemstones. Examples of allochromatic characteristics or colour by impurities is given below;

1. Beryllium (Be): Emerald (blue-green) 2. Chromium (Cr): Emerald, Tourmaline (green) 3. Copper (Cu): Malachite (green) 4. Iron (Fe): Aquamarine, Tourmaline (green); Chrysoberyl, Citrine, (green-yellow-brown) 5. Lithium (Li): Tourmaline (green, pink) 6. Manganese (Mn): Tourmaline (pink), Morganite 7. Titanium (Ti): Sapphire (blue) 8. Vanadium (V): Emerald, (green-red), Tourmaline (green)

Amazonite

Amazonite is an easily fracturing green feldspar that can be cut and polished to be used as

gemstone. Its colour is believed to be coming from lead and water.

Figure 2: Amazonite specimens (Source: www.gemstone-dictionary.com)

This mineral is common at Kabumba in Mzimba and Usisya in Nkhata Bay hosted by granitic rocks.

Apatite

Apatite is a calcium phosphate rock containing fluorine, chlorine and vanadium among other

elements that substitute for calcium. Its colour varies from green to blue and can be mistaken for

aquamarine and tourmaline. The immediate differentiation is that it is softer.

Figure 3: Example of pegmatite apatite (www.geologycafe.com)

Gem apatite has been mined in Nsanje around Tengani and Lulwe mission.

Beryl

Beryl is a rare mineral that is rich in beryllium and occurs in veins and cavities associated with

hydrothermal activity within pegmatites. These minerals are in veins that penetrate quartz rocks in

the order of mica, feldspar and beryl in quartz.

Beryl which is non gem quality is a source of beryllium and is sold as “trash”. The gem quality has

usually uniform colour, is transparent and with less or no cracks for easy cutting and polishing.

Figure 4: Beryl crystals from Kacheure mine in Mzimba

This mineral occurs in eight colours with different following names: emerald (green), aquamarine

(greenish blue to blue), morganite (pink to orange), red beryl (red), heliodor (yellow to greenish

yellow), maxixe (deep blue), goshenite (colourless), and green beryl (light green). The common

gemstone from this mineral is aquamarine whose colour ranges from blue to milky blue.

Garnet

Garnet is found in pegmatites as an accessory mineral. The common garnet in Malawi pegmatite is

red garnet called almandine and orange garnet called spessartine. While the author was undertaking

limestone exploration on Malowa hill (Golomoti) in 1996, he found green garnet in a pegmatite on

easten summit.

Quartz

Quartz is a hard, durable and common mineral that forms a massive principle component of a

pegmatite. Gem varieties include amethyst, smoky quartz and rose quartz. These are grouped as semi-

precious stones.

Amethyst forms through radiation from surrounding rocks activating

colour centres around iron impurities.

Smoky quartz derives its colour through natural radiation emitted

from the surrounding rock. This radiation activates colour centers

around aluminum impurities within the crystalline quartz. These

gems can be processed and used in rings, cufflinks, pendants,

necklaces, earrings, and brooches for people who like the yellowish

brown to brown color.

Figure 5: A typical crystal of smoky quartz

The color of rose quartz is attributed to microscopic inclusions of a pink variety of the mineral

dumortierite. Rose quartz is usually cut into cabochons and beads.

Amethyst is common in Mzimba and Chitipa.

Smoky quartz is collected from pegmatite cavities

on Mulanje mountain, Zomba mountain and Nyika

plateau where they are sold as mineral specimens.

Rose quartz occurs as pockets within massive

white quartz in Mzimba.

Tourmaline

Tourmaline is a multi-coloured gem falling within semi-precious stones. It is crystalline boron silicate

mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or

potassium.

Figure 7: The multi-coloured nature of tourmaline

RARE MINERALS

Pegmatite hosts many rare minerals. In Malawi a few minerals have been observed so far. These contain beryllium, columbium, niobium, tantalum and titanium, tungsten and many other elements. In most cases these have included columbo-tantalite, pyrochlore, beryl, rutile and ilmenite. If the mine

Figure 6: Rose quartz from Kacheure mine in Mzimba

contains nice crystals, the minerals are often more valuable as mineral specimens and faceted or tumbled. Good sources of these minerals are Mzimba, Senzani, Neno, Thambani and Tengani areas.

INDUSTRIAL MINERALS

Pegmatite can be a source of industrial minerals such as;

1. Sheets of mica as initially explored in Mzimba pegmatites, 2. Feldspar for use in glass and ceramic use for example in the Linthipe and Kirk Range area 3. Quartz for use in glass making, abrasive and foundry sand

CONCLUSION

Malawi is country that requires a serious business minded leadership if we are to unveil earths

treasure. A systematic mineral exploration program is required grouped according to geological

prospectivity as well as taking into account the financial and human resource allocation. Pegmatites

prospecting and support to small scale miners will being order and sustainable mining that will

generate mineral wealth and sustainable environmental management and poverty alleviation.